Trauma Management - Part 2

29th January, 2007


Part 1 of this series considered the initial priorities of trauma management. This follow up paper focuses on understanding the mechanisms of injury (MOIs) that help the nurse to recognise potentially serious injuries which may otherwise have been overlooked.

An understanding of the principles behind the study of mechanism of injury is necessary.

Energy Laws

Blood on instruments from an emergencyNewton’s First Law of Motion states that:

  1. A body at rest or a body in motion will remain in that state until acted upon by an outside force
  2. In a vehicle travelling at 50 mph, the occupant is also travelling at 50 mph
  3. When the car stops, the occupant continues to travel at 50mph until some force acts on the occupant (Driscoll, Skinner & Earlam, 2000).

Conservation of energy

Energy cannot be created nor destroyed – however, it can be changed in form. Energy can be absorbed producing deformation of the substance that it connects with (Di Maio, 2000).

Kinetic energy (KE)

Kinetic Energy or KE is equal to twice the mass of the object multiplied by the velocity (speed) of the object squared (Mass/2 x V2). It is the velocity (V) which infl uences the overall KE more than mass, since the greater the speed, the more energy is generated (Di Maio, 2000).


  1. Force = Mass x Acceleration
  2. Force = Mass x Deceleration
  3. Mass x Acceleration = Force = Mass x Deceleration

Simply put, to accelerate a bullet from a the muzzle of a weapon requires the force from the explosion of the gunpowder; once the bullet is set in motion by this explosion, an equal amount of tissue destruction must occur inside the body to stop it as was used to start it (Di Maio, 2000).

Energy law summary

  1. Motion is created by force (energy exchange)
  2. Force (energy exchange) must stop this motion
  3. If such energy exchange occurs inside the body tissue damage is produced.

The mechanism of injury (MOI) can be divided into four distinct categories:

  • Blunt
  • Penetrating
  • Thermal
  • Blast

Single accidents/ traumatic incidents may incorporate all of these MOIs, however, the common factor in all of these is that the extent of the injury is determinant upon the energy transferred to the tissues as described above (Driscoll, Skinner & Earlam, 2000).

Other factors in determining the amount of damage are:

  • Surface area
  • Length of time exposed to energy
  • Type of tissue to which energy is applied
  • Adult or child (children more likely to be seriously injured due to their proportionate size).
    Injuries from Different Mechanical Forces
    Mechanism Of InjuryPotential injuries
    Frontal impact: bent steering wheel, knee imprint in dashboard, bulls-eye fracture of windscreenCervical spine fracture, anterior flail, myocardial contusion, pneumothorax, transection of aorta, ruptured liver/spleen, posterior fracture/dislocation of hip and/orknee
    Side impact

    Contralateral neck strain, cervical spine fracture, lateral flail, pneumothorax, ruptured spleen/liver (depending on side of impact), # of pelvis/acetabulum
    Rear impactCervical spine injury
    Ejection from vehiclePrecludes meaningful prediction of injury patterns but places patient at greater risk from virtually all injury mechanisms - mortality significantly increased
    Motor vehicle-pedestrianHead injury, thoracic and abdominal injuries, fractures of the lower extremities

Blunt MOI

According to Eaton (1999) blunt trauma is the most common MOI seen in the UK and can be subclassifi ed into three forces involved in the energy transfer:

  • Direct impact/ compression – seen commonly in RTIs
  • Shear – seen commonly in falls from height
  • Rotation – seen commonly in industrial injuries.

Penetrating MOI

This particular type of trauma is mainly confined to assaults (Greaves, Porter & Ryan, 2001). This type can also be split into three sub-classifi cations:

  • Low Energy – seen in knife and similar type wounds
  • Medium Energy – seen in handgun wounds
  • High Energy – seen in assault rifl e wounds (military).

Thermal MOI

This particular type of MOI is dependant upon the factors described that determine injury such as time exposed to source of
energy, size of area exposed to energy and the type of tissue the thermal energy is applied to.

There are many effects of the blast and these are broken down into the following:

  • Primary – direct effect of the blast wave where hollow organs are particularly vulnerable
  • Secondary – due to fragments where injury is from medium to high energy missiles
  • Tertiary – causes gross displacement of body, resulting in amputation in some cases
  • Crush injuries – blunt trauma as result of environmental factors
  • Burns – nature of energy involved in blast
  • Psychological effects – post traumatic stress disorder (PTSD) following bomb blasts, shell shock in mass
    casualty situation may mask other injuries.

According to Greaves et al (2001) trauma is a major cause of death in the under 35 year age group. Road traffi c incidents are the leading cause of trauma, therefore, an understanding on the MOI resulting from such incidents may result in a drop in the preventable fatalities from this type of trauma.

The majority of serious road traffic incidents result in blunt trauma, mostly due to direction of impact, damage sustained by the car and, in particular, damage to the passenger compartment, gives an indication of likely injury. Below is a table that briefly outlines the potential injuries associated with this common MOI.


A clear understanding of all the aspects of MOI is most important for both pre-hospital care teams and those based at A&E. As part of a pre-hospital response team, you may be expected to handover the scene and detail what happened in order to build the accurate picture of injuries sustained simply by MOI alone.


This article has presented the background to mechanisms of injury that will assist nurses to recognise potentially serious injuries. The physical laws which govern these mechanisms may require some further reading and may become more relevant to those involved with mobile medical/surgical teams or pre-hospital care. In the third and fi nal part of this series on trauma management the most appropriate treatment shall be examined.

Part 3 will go on to examine the various treatments appropriate to specific situations.


Eaton JC (1999). Essentials of Immediate Medical Care. (2nd Ed), Edinburgh: Churchill Livingstone.
Di Maio, V.J.M. (2000). Gunshot Wounds. (2nd Ed). New York. CRC Press.
Driscoll, P., Skinner, D. & Earlam, R. (2000). ABC of Major Trauma.(3rd Ed). London. BMJ Publishing.
Greaves I, Porter K, Ryan J(2001). Trauma Care Manual.London: Arnold Publishing.

Dr Greig Ferguson, MD, DSc, BN(Hons), Dip IMC RCSEd, ALS, ATLS, PHTLS,
Tutor CB Training Ltd.